Sildenafil comes as a tablet, capsule, chewable or oral jelly to take by mouth.

If you are taking sildenafil to treat erectile dysfunction, follow your doctor's directions and the guidelines in this paragraph. Take sildenafil as needed before sexual activity. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Sildenafil usually should not be taken more than once every 24 hours. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. You can take sildenafil with or without food. However, if you take sildenafil with a high-fat meal, it will take longer for the medication to start to work.

If you are taking sildenafil to treat PAH, follow your doctor's directions and the guidelines in this paragraph. You will probably take sildenafil three times a day with or without food. Take sildenafil at around the same times every day, and space your doses about 4 to 6 hours apart.

Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take sildenafil exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on an average dose of sildenafil and increase or decrease your dose depending on your response to the medication. Tell your doctor if sildenafil is not working well or if you are experiencing side effects.

If you are taking sildenafil for PAH, you should know that sildenafil controls PAH but does not cure it. Continue to take sildenafil even if you feel well. Do not stop taking sildenafil without talking to your doctor.

Ask your pharmacist or doctor for a copy of the manufacturer's information for the patient.
Other uses for this medicine

This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.

What special precautions should I follow?

Before taking sildenafil,

tell your doctor and pharmacist if you are allergic to sildenafil or any other medications.

do not take sildenafil if you are taking or have recently taken nitrates (medications for chest pain) such as isosorbide dinitrate (Isordil), isosorbide mononitrate (Imdur, ISMO), and nitroglycerin (Nitro-BID, Nitro-Dur, Nitroquick, Nitrostat, others). Nitrates come as tablets, sublingual (under the tongue) tablets, sprays, patches, pastes, and ointments. Ask your doctor if you are not sure whether any of your medications contain nitrates.

do not take street drugs containing nitrates such as amyl nitrate and butyl nitrate ('poppers') while taking sildenafil.

tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take. Be sure to mention any of the following: alpha blockers such as alfuzosin (Uroxatral), doxazosin (Cardura), prazosin (Minipress), tamsulosin (Flomax), and terazosin (Hytrin); amlodipine (Norvasc); certain antifungals such as itraconazole (Sporanox) and ketoconazole (Nizoral); anticoagulants ('blood thinners') such as warfarin (Coumadin); certain barbiturates such as butalbital (in Esgic-Plus, in Fioricet, in Fiorinal, others) and secobarbital (Seconal); beta blockers such as atenolol (Tenormin), labetalol (Normodyne), metoprolol (Lopressor, Toprol XL), nadolol (Corgard), and propranolol (Inderal); bosentan (Tracleer); cimetidine (Tagamet);efavirenz (Sustiva); erythromycin (E.E.S., E-Mycin, Erythrocin); HIV protease inhibitors including amprenavir (Agenerase), atazanavir (Reyataz), darunavir (Prezista), fosamprenavir (Lexiva), indinavir (Crixivan), lopinavir (in Kaletra), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), saquinavir (Fortovase, Invirase), and tipranavir (Aptivus); nevirapine (Viramune); other medications or devices to treat erectile dysfunction;medications for high blood pressure; certain medications for seizures including carbamazepine (Carbatrol, Epitol, Tegretol), phenobarbital, and phenytoin (Dilantin, Phenytek); rifabutin (Mycobutin); and rifampin (Rifadin, Rimactane). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with sildenafil, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.

tell your doctor what herbal products you are taking or plan to take, especially St. John's wort.

tell your doctor if you smoke, if you have ever had an erection that lasted for several hours, and if you have recently lost a large amount of body fluids (dehydration). This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Also tell your doctor if you have or have ever had pulmonary veno-occlusive disease (PVOD; blockage of veins in the lungs); a stomach ulcer; heart, kidney, or liver disease; a heart attack; an irregular heartbeat; a stroke; chest pain; high or low blood pressure; high cholesterol; a bleeding disorder; blood circulation problems;blood cell problems such as sickle cell anemia (a disease of the red blood cells), multiple myeloma (cancer of the plasma cells), or leukemia (cancer of the white blood cells); conditions affecting the shape of the penis (e.g., angulation, cavernosal fibrosis, or Peyronie's disease); or diabetes. Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa (an inherited eye condition that causes loss of vision) or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see.

tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking sildenafil, call your doctor.

if you are having surgery, including dental surgery, tell your doctor or dentist that you are taking sildenafil.

if you are taking sildenafil to treat erectile dysfunction, tell your doctor if you have ever been advised by a health care professional to avoid sexual activity for medical reasons or if you have ever experienced chest pain during sexual activity. Sexual activity may be a strain on your heart, especially if you have heart disease. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise.

tell all your health care providers that you are taking sildenafil. If you ever need emergency medical treatment for a heart problem, the health care providers who treat you will need to know when you last took sildenafil.

What special dietary instructions should I follow?

Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.
What should I do if I forget a dose?

If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule.

If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What side effects can this medication cause?

Sildenafil may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

headache

heartburn

diarrhea

flushing (feeling of warmth)

nosebleeds

difficulty falling asleep or staying asleep

numbness, burning, or tingling in the arms, hands, feet, or legs

muscle aches

changes in color vision (seeing a blue tinge on objects or having difficulty telling the difference between blue and green)

sensitivity to light

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:

sudden severe loss of vision (see below for more information)

blurred vision

sudden decrease or loss of hearing

ringing in ears

erection that is painful or lasts longer than 4 hours

dizziness or lightheadedness

fainting

chest pain

worsening shortness of breath

itching or burning during urination

rash

Some patients experienced a sudden loss of some or all of their vision after they took sildenafil or other medications that are similar to sildenafil. The vision loss was permanent in some cases. It is not known if the vision loss was caused by the medication. If you experience a sudden loss of vision while you are taking sildenafil, call your doctor immediately. Do not take any more doses of sildenafil or similar medications such as tadalafil (Cialis) or vardenafil (Levitra) until you talk to your doctor.

There have been reports of heart attack, stroke, irregular heartbeat, bleeding in the brain or lungs, high blood pressure, and sudden death in men who took sildenafil for erectile dysfunction. Most, but not all, of these people had heart problems before taking sildenafil. It is not known whether these events were caused by sildenafil, sexual activity, heart disease, or a combination of these and other causes.Talk to your doctor about the risks of taking sildenafil.

Some patients experienced a sudden decrease or loss of hearing after they took sildenafil or other medications that are similar to sildenafil. The hearing loss usually involved only one ear and may not get better. It is not known if the hearing loss was caused by the medication. If you experience a sudden loss of hearing, sometimes with ringing in the ears or dizziness, while you are taking sildenafil, call your doctor immediately. If you are taking sildenafil (Viagra) for erectile dysfunction, do not take any more doses of sildenafil (Viagra) or similar medications such as tadalafil (Cialis) or vardenafil (Levitra) until you talk to your doctor. If you are taking sildenafil (Revatio) for PAH, do not stop taking your medication until you talk to your doctor.

Sildenafil may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.